Lines or other edges drawn on pixelated video displays are prone to “jaggy” artifacts, where the viewer can see the edge stair-step between the pixels that are drawn with color of the item and the color of the area around the item. For example, if a black box is displayed at a rotation angle of 45 degrees on a white background, all of the edges of the box will have a visible saw-tooth edge if a user of a computing device looks closely. This is a natural outcome of using displays with discrete pixels, because there is no practical way to represent on such displays a continuous line that is diagonal to the pixel layout. Instead, a line is represented just a series of separate pixels, or small rectangular (usually square) areas on the display surface. In short, drawing with squares is not smooth.
This artifact is present in general, but can be particularly noticeable when the pixels on a display are relatively large (for example, on low-resolution or low-dpi displays). The artifact may also be particularly noticeable when a line is drawn at a small angle relative to the pixel layout (e.g., lines close to, but not on, the horizontal and vertical), because the steps are particularly long in such a situation. The problem is how to make lines look smoother, or “antialiased.” General antialiasing techniques involve having some pixels represent partial coverage of a line by having translucent variations of the line color. The net effect is that the line “fades out” at the edges, and looks smoother by avoiding having such hard edges between the on-the-line and off-the-line pixels on the display along the stair-step or saw-tooth edge.